Lead isotopic composition from data of high-precession MC-ICP-MS and sources of matter in the large-scale Sukhoi Log noble metal deposit,Russia |
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| Authors: | I V Chernyshev A V Chugaev Yu G Safonov M R Saroyan M A Yudovskaya A V Eremina |
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| Institution: | 1.Institute of Geology of Ore Deposits, Petrography, Mineralogy, and Geochemistry,Russian Academy of Sciences,Moscow,Russia |
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| Abstract: | The lead isotopic composition of 33 sulfide samples from orebodies of the Sukhoi Log deposit was studied by high-precession
MC-ICP-MS with a precision of ±0.02% (±2SD from 120 analyses of the SRM 981 standard sample). The deposit is located in the
Bodaibo gold mining district in the northern Baikal-Patom Highland. Gold mineralization is hosted in Neoproterosoic black
slates. Variations of lead isotope ratios of the Sukhoi Log sulfides are generally typical of Phanerozoic deposits and ore
fields. They are significant for 206Pb/204Pb (17.903–18.674), moderate for 208Pb/204Pb (37.822–38.457), and relatively narrow for 207Pb/204Pb (15.555–15.679). In the Pb-Pb isotope diagrams, the data points of pyrite and galena constitute a linear trend. The points
corresponding to pyrite from metasomatic ore occupy the left lower part of the trend. Galena from late gold-quartz veins shows
more radiogenic Pb, and corresponding data points are located in the upper part of the trend. According to the Stacey-Kramers
model, the end points of the trend, which is regarded as a mixing line, have μ2 = 9.6 and μ2 = 13.2 and model Pb-Pb ages 455 and 130 Ma, respectively. The isotope characteristics of ore lead, their relationships in
pyrite and galena, and the mixing trend of Pb isotopic compositions are clearly tied to two Paleozoic stages in the formation
of the Sukhoi Log deposit (447 ± 6 and 321 ± 14Ma) and testify to the leading role of crustal sources, which are suggested
as being the Neoproterozoic black-shale terrigenous-carbonate rocks. |
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